Economics of scale make Ethernet (IEEE 802.3) and IP (internet protocol) technology (as defined by the Internet Society and the Internet Architecture Board, basic IP protocol being RFC 791) an interesting solution for all digital communication, wired and wireless, large and limited bandwidth, real-time traffic, reliable transmissions, etc . . .
An essential element of digital networking is the addressing, which follows a layered approach as in OSI (Open Systems Interconnection standard of the ISO) network layering.
At the data link layer Ethernet MAC (Media Access Control) addresses are used. They are used between machines on the same local area network. At the network layer IP addresses are used. They are known and used by the endpoints of the connection on an internet. Router nodes on the network connect local area networks to route IP datagrams to their destination, based on routing information.
While the original purpose was to have a unique IP address for each end node in the network, IP network address translation (RFC 1631) has been introduced to allow for networks with end nodes that have IP addresses that are not globally known or unique, to connect to a global internet by having their IP address in IP datagrams rewritten to a globally assigned unique IP address. This defines a hierarchy in IP addressing. The hierarchy is limited to two levels: global addresses and local addresses. No provisions are available for a further split up of the local addresses.
The IP network architecture is robust to configuration changes, based on auto-learning mechanisms with time-outs on learned information. For the local area network this is the ARP protocol (address resolution protocol RFC 826) and for the global network, the routing protocols (such as the OSPF protocol RFC 1247). The time scale to which these protocols react to configuration changes ranges from several minutes to several hours. During these times inconsistencies are possible. Shortening these times would either jeopardise the robustness of the network or involve a large messaging overhead.
The domain name system (DNS RFC 1034 and 1035) adds a logical addressing layer on top of the IP addresses. Apart from the convenience of textual addressing it adds flexibility, especially to add multiple overlay addressing hierarchies, possibly referring to the same IP addresses. The DNS addressing mechanism has been a preferred addressing layer to render configuration changes. Dynamic update in DNS (RFC 2136) allows for synchronous instead of periodic update of the addressing information in the DNS database. Here also the lower timeouts encompass an extra messaging overhead. More specifically, removing the possibility of cached DNS information adds extra delay to the connection set-up. A more severe limitation of this approach is that all client software has to obey this no-caching policy and that the configuration change only propagates to new connections. Again this could be coped with in the client applications, but this would require specific software to be added and would also involve extra messaging.
In the paper ‘IP addressing playing the numbers. IP addresses are in short supply’ (W. Dutcher, Data Communications, vol. 26, no. 4, Mar. 21, 1997) the author discusses the shortage of IP addresses. One way to translate private addresses into public addresses when they are sent to the Internet, is to use network address translation (NAT) in routers or firewalls. Using NAT all private addresses of outbound traffic (towards the Internet) are taken and the source addresses are converted. For inbound traffic (towards the internal network) the process works in reverse.
More and more trains are nowadays equipped with 100 Mbit/s (or faster) Ethernet backbones. On board devices communicate with each other by means of different protocols using the Ethernet backbone (UDP, TCP/IP, etc . . . ). For addressing the different devices, IP addresses are being used. Due to reasons related to network availability the use of trainwide (redundant) dynamic host configuration protocol (DHCP) servers is dissuaded. A reliable network topology discovery with deterministic, logical and location based IP address assignment is required and is indeed available on the market now.
Document EP1694035-A1 discloses a solution for reliable packet routing in a hierarchical reconfigurable network. A transportation vehicle (e.g. a train) is considered comprising a plurality of ‘cars’. Each car comprises a computer network referred to as a sub-network. Individual cars can be combined in sub-compositions (units) whereby the sub-networks get concatenated. The number of cars in such a sub-composition as well as the arrangement of the cars, is variable. Hence, the reconfigurable network has a dynamic nature. Several sub-compositions may be combined variably and interconnected to form larger compositions. The full vehicle composition is arranged with a network composed of sub-networks defined at lower level in the hierarchy. A hierarchical addressing scheme is applied, wherein the address is adapted based on the hierarchy level of the destination network. The proposed solution in EP1694035 allows for the assignment of IP addresses in a logical way without human intervention.
However, there remains an unsolved problem about dynamic host configuration for daisy chain nodes. The major advantage of using daisy chained network topologies is clearly the reduced amount of wiring that is required as compared to other topologies. Hence, there is a reduction in cost and weight. A node is to be understood as a device with one Ethernet input and one Ethernet output, whereby switching means are provided to short the input and/or output in case of a failure. The problem is illustrated in FIG. 1. The figure depicts two Ethernet nodes (299,399). Each of those nodes is composed as follows. The node comprises or is connected to an application (200) via an Ethernet switch (210) adapted for exchanging communication data with the application (200) and the Ethernet network (400). This switch allows traffic from the application to be communicated to the Ethernet network (400) and receives data addressed to the application and forwards this accordingly. Additionally, this device forwards packets between the IN and the OUT ports if the data packages are not uniquely addressed to the application. If for some reason (power failure, software crash, . . . ) the application is no longer operational (or was not operational since the start-up) switching means (220) are closed automatically to ensure that communication is still possible from the backbone (900) of the train over the local backbone switch or router (100) to the devices in the daisy chain which are still operational. In the example illustrated in FIG. 1 this is node 399. Note that the dashed line connecting two switch means (220) indicates that those switching means are interconnected and open and close simultaneously at all times. The switching means are typically implemented as a relay, as shown in FIG. 1. Other circuitry to connect or disconnect the Ethernet switch from the daisy chain could be applied as well (e.g. use of a solid state switch).
Following the addressing mechanism described in EP1694035 a node receives an IP address which is a function of the train unit number, car number and type of node and switch port number. Note that hereby a transportation vehicle with hierarchical configuration is considered as in the above-mentioned document EP1694035. This allows addressing Ethernet nodes in a logical manner, depending on how a train has been assembled (i.e. depending on the topology), without human intervention. In normal condition node (299) at location (1) should be assigned address IP(1) and node (399) at location (2) should receive address IP(2). This has been depicted as case A in FIG. 1. Because of the nature of the Ethernet switch (210, 310), without provisions, the backbone switch/router (100) will not be able to retrieve the location of the nodes in the daisy chain. Even specific software solutions or solutions based on Dynamic Host Configuration Protocol (DHCP) option 82 do not solve the problem when in the initial state one or more daisy chained nodes are malfunctioning at the time IP addresses are assigned to the different nodes. In case of FIG. 1 the switch only sees one node (399) and assigns the first IP address IP(1) reserved for the chain at port (110) to the second node (399) in the chain (represented as Case B in FIG. 1). The aim however was the assignment of addresses as being depicted in Case A in FIG. 1. Hence, in case of a malfunctioning node the requirement that an IP address be location based is immediately broken.
In the prior art the use of MAC/IP tables in routers is known, but such a solution suffers from the drawback of requiring manual configuration if the network topology changes or network devices are replaced.
Solutions based on Dynamic Host Configuration Protocol (DHCP) option 82, whereby topology is taken into account, require special hardware. As stated, this method does not solve the problem of malfunctioning devices in the chain during the assignment process. Application US2009/279454, which is also concerned with unambiguous assignment and IP address allocation, provides an example.
Patent document EP 0983905 B1 discloses a circuit arrangement for decoupling an electronic device from a data line in a motor vehicle over which information is exchanged.